In recent years, applications of image forming apparatus such as electrophotographic copying machines and others have been expanding, and there has been an increasing demand in the market for a higher level of image quality. Particularly, with respect to office documents and others, in addition to the development of image copying techniques and latent image-forming techniques at the time of inputting, also at the time of outputting, the types of hieroglyphic characters have become richer and more refined, and due to dissemination and development of presentation software, reproducibility of latent images of extremely high quality is desired so that there will be few defects or unsharpness in printed images. Particularly, as the developer to be used in a case where latent images on a latent image substrate constituting an image forming apparatus are line images of 100 μm or less (about 300 dpi or more), a conventional toner having a large particle size is usually poor in reproducibility of such fine lines, whereby the sharpness of line images has not yet been sufficient.
For improving image quality, it is effective to reduce the particle size of toner, and a chemical toner is suitable for this technique, and various types of toners have been developed (Patent References 1 to 12). In particular, chemical toners having a narrow particle size distribution can be produced and their charging properties can be homogenized, and therefore, chemical toners are advantageous for electrophotographic process.